High sound levels in work settings can have negative effects on worker concentration and productivity as noise can be a distraction. Even office spaces with offices separated by walls and doors transmit sound between them. As office buildings optimize space use, the outcomes often result in a decrease of the average amount of space allotted for each person, office, or work area. With more office workers in a given area, the noise levels in that area are increasing beyond acceptable levels.
Some gains in controlling unwanted sound transmission can be made by addressing the composition or construction of the walls and doors that separate adjacent spaces. In addition, any voids or penetrations which could transfer sound between an office and the adjoining spaces that can also be sealed or insulated. However, these more conventional approaches still do not deliver the degree of sound mitigation often desired in a work setting.
Within the space above the suspended interior ceiling, many modern office buildings often have a plenum cavity common to a number of offices and adjoining spaces. The plenum cavity is typically an unconditioned horizontal space usually encompassing the entire ceiling area of a floor. The purpose of the ceiling plenum is to house building infrastructure systems such as heating, air conditioning, ventilating, lighting, cabling, fire sprinkler, telecommunications and/or structural elements, among some of the more common elements. The ceiling plenum is considered a non-occupiable area and is enclosed at its base by the suspended ceiling system which consists of the suspended ceiling grid and the lay-in tiles of the grid. In addition, this ceiling assembly is penetrated by various items such as: light fixtures, air supply and return devices, sprinkler heads, telecommunication devices and fire egress devices. Given the nature of conventional suspended ceiling assemblies and the plenum spaces which they create, occupied work areas on a given floor are subjected to various penetrations. Each penetration is a potential area for sound transmission allowing sound to carry from one work area to another through the ceiling plenum and the various penetrations within the suspended ceiling assembly. The ceiling openings, which are typically fitted with return air grilles, are designed to allow air flow back into the plenum naturally allowing ventilation of occupied spaces via air flow. This method of air return has been conventionally applied to commercial office buildings since the beginning of the 20th century and is recognized as a viable, cost effective method. These return air grilles also act as pathways by which sound travels from one occupied office through the ceiling plenum to another occupied office.
Prior efforts to reduce unwanted sound transmission through return air grilles have had limited success. Providing enclosed ducting for each return air grille is costly and time consuming to install, and is often not feasible due to vertical space constraints within the plenum. In addition, installers are required to enter the plenum with frequency to address maintenance of the buildings systems housed in this area. The plenum areas can be dusty and have other debris—a common condition in buildings which, when disturbed, can create unacceptable air quality conditions for workers. Conventional sound attenuators positioned over return air grilles or other lay-in ceiling penetrations have not proven to provide a cost effective reduction in unwanted sound transmission, tend to be heavy stressing the lay-in ceiling grid, are often bulky to handle and install, and are an impediment when accessing the ceiling plenum for routine maintenance throughout the life-cycle of the building.